25.
SHIELD TUNNELLING METHOD
This method involves the use of shield machine to
drive the tunnels below the ground.
After completion of a work shaft, the shield machine
is lowered into the shaft and assembled there before
excavation and construction of the tunnels using
precast concrete lining segments of about 1.2 meter
width.
This construction method causes minimal disruption
to traffic and the environment because all the work
takes place below ground and the ground level
environment is unaffected.
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27.
CUT and COVER TUNNELLING METHOD
This construction method, whereby the site is fully
excavated, the structure built and then covered over,
uses diaphragm walls as temporary retaining walls
within the site area.
Step one :Construction of diaphragm walls, pin piles,
and decking.
Step two :Excavation within the diaphragm walls,
installing struts as work progresses.
Step three :Construction of permanent floor slabs and
walls.
Step four : Fitting out the internal structures,
backfilling, and reinstating the surface structures.
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30.
1- Mechanical Support TBM
A mechanical-support TBM has a full-face
cutterhead which provides face support by
constantly pushing the excavated material
ahead of the cutterhead against the
surrounding ground.
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31.
2- Compressed-Air TBM
A compressed-air TBM can have either a full-
face cutterhead or excavating arms.
Confinement is achieved by pressurizing the
air in the cutter chamber.
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36.
Effect of faults: the relation between the fault
slope direction and the tunnel direction, width of
the fault zone, type and thickness of the fill
material and the hydrostatic pressures in both
sides of the fault are some problems in the
tunnelling.
Relation between the fault zone and the tunnel
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37.
Tunnel excavations in the slopes: the
discontinuities (layers, fissures) inclined inside or
outside of the slope are very important regarding the
stress and strength of the tunnel.
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38.
Effect of the folds: While tunnel is excavated in an
area that contains folded rocks, different stresses and
conditions may occur depending on the fold type.
Fold axis and the tunnel direction is parallel
Fold axis and the tunnel direction is vertical
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40.
Classification of rocks for engineering
purposes is needed in analyzing the project
costs and to obtain an economic and reliable
solution.
The classification of the rocks, that the tunnel
will be constructed in, is first done by
Terzaghi. But, it is too general and gives
qualitative results.
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